For the purpose of improving color rendering properties of a white LED or improving color reproducibility in the case where a white LED is used as back light of liquid crystal displays, there is needed a phosphor that is excited with light corresponding to near-ultraviolet to blue LEDs to emit red light, for which studies are now being in progress. In JP-T 2009-528429 corresponding to WO 2007/100824 (Patent Document 1), a complex fluoride phosphor, in which Mn is added to a complex fluoride represented by the formula of A2MF6 wherein A represents Na, K, Rb or the like and M represents Si, Ge, Ti or the like, is stated as useful.
In recent years, on the other hand, there is a technical demand for increasing a light flux per unit white LED, for which an attempt has been made to increase an amount of current flowing in the LED chip. In this attempt, a phosphor is continuously exposed to intense excitation light (such as of blue color) with the possibility that the temperature rises. As a consequence, it has been found that the light emission of the phosphor lowers during a long period of time, and there occurs a phenomenon of changing the color of a white LED or reducing the light flux.
Aside from the above Patent Document 1, in related art according to the present invention is indicated in U.S. Pat. No. 3,576,756 (Patent Document 2), JP 4582259 corresponding to US 2013/271960 (A1) (Patent Document 3), JP-A 2012-224536 corresponding to US 2012/256125 (A1) (Patent Document 4), and JP-A 2014-141684 corresponding to EP 2774966 (A1) (Patent Document 5).